1. As part of a study investigating the effect of dietary alterations of sodium and potassium intake on blood pressure, the changes in nutrients that occurred with dietary intervention were determined.
2. Mild hypertensive subjects were randomized to one of four dietary intervention groups: control; high potassium; low sodium; low sodium, high potassium. The changes in nutrients in each diet group were assessed by dietary history and five repeat 24 h dietary recalls. Assessment was validated by measurement of urinary nitrogen excretion and urinary electrolytes.
3. The three dietary intervention groups experienced a fall in blood pressure (systolic: 4.4 ± 1.0 mmHg, P<0.005; diastolic: 3.3 ± 0.7 mmHg, P<0.001), greater than that observed in the control group.
4. The only significant dietary change across all diet groups was a reduction in the dietary sodium/potassium ratio, which was significantly less than that of the control group. The only other nutrient to differ from the control in all groups was fat intake, which was reduced.
5. In the control group there was a small but significant decrease in energy, fibre, protein, carbohydrate, potassium and magnesium intake. In the high potassium group there was a significant increase in fibre, carbohydrate, potassium, magnesium, and a decrease in calcium intake. In the low sodium group there was a decrease in energy intake with a subsequent reduction in all nutrients except alcohol. In the low sodium, high potassium group there was a significant reduction in dietary sodium and protein and an increase in fibre, carbohydrate, potassium and magnesium.
6. The reduction of the dietary sodium/potassium ratio correlated with a reduction in the urinary sodium/potassium ratio. This was the best predictor for change in diastolic pressure in all groups, suggesting that reduction in the sodium/potassium ratio contributed to the fall in blood pressure.
7. Reduction of sodium intake and increase in potassium intake by dietary means caused a reduction in blood pressure which does not appear to be due to alteration of other measured dietary constituents.